1. Field of the Invention
The present invention relates to an induction heating furnace for melting metals through induction heating and a bottom tapping mechanism thereof.
2. Description of the Related Art
In the case of producing a high purity metal or a metal alloy of desired components by melting a high reactive metal, attention has focused on an induction heating furnace which is capable of ensuring an uniform temperature over the entirety of a molten metal by induction heating and agitation to prevent variations in quality, and also suppressing the mixing of impurities into the molten metal to a low level, to prevent reduction in quality.
A conventional induction heating furnace has a side wall extending so obliquely as to increase an aperture from a bottom having a tapping portion to a certain point and then rising up vertically therefrom to an upper edge with the aperture kept at a constant diameter, as disclosed by, for example, Japanese Laid-open Patent No. Hei 4(1992)-327342. The side wall is formed by a plurality of longitudinally split, conductive segments arrayed circumferentially and insulated from each other. At the outer periphery of the side wall, an induction coil is arranged so that a metal at the inside of the side wall can be heated by induction heating. The tapping portion is provided with a mold to which a tapping passageway is communicated vertically. With the induction heating furnace thus constructed, the metal is melted by induction heating and then the molten metal flows into the tapping passageway of the mold, so as to be taken out with being solidified.
Also, Japanese Laid-open Patent No. Hei 8(1996)-145571 discloses an induction heating furnace including a side wall rising up vertically from a flat bottom having a tapping portion to an upper end, with an aperture kept at a constant diameter; and a bottom lid for closing the tapping portion. This induction heating furnace is so designed that when metal is melted by induction heating, the bottom lid can be melted to open the tapping portion, so as to take out the molten metal.
With the former arrangement in which the mold is provided at the tapping portion, a solidified layer in the tapping passageway in the mold and a solidified layer on the side wall become connected with each other. Due to this, taking out the metal from the mold requires a very large drawing force, thus causing difficulties in taking it out. Also, with the latter arrangement in which the tapping portion is closed with the bottom lid, once the bottom lid is melted to open the tapping portion, the tapping portion cannot be closed until all molten metal has completely been taken out. Due to this, switching between the melting of the metal and taking out the molten metal cannot be made smoothly. In short, the conventional type arrangements have a first problem that the melting of the metal and the task of taking out the molten metal cannot be made with ease and the switching operation between the melting of metal and taking out the molten metal cannot be made smoothly.
Further, where the side wall rises up with the aperture kept at a constant diameter, as in the above-described arrangement, when metallic vapor evaporates from the molten metal surface or the components of the gas produced in the molten metal dissipates from the molten metal surface, the evaporating direction of the metallic vapor or the rising direction of the gas become parallel to a wall surface of the side wall. Thus, the conventional arrangements have the second problem that the metal easily adheres to the side wall, thus requiring labor in the cleaning of the side wall, while the gas readily contacts the side wall to increase the flow resistance of the exhaust gas, which hinders the gas from being fully eliminated and causes a reduction of quality.